package Easy.Tree;

//给定一个二叉树，判断它是否是 平衡二叉树
//
// 示例 1：
//输入：root = [3,9,20,null,null,15,7]
//输出：true
//
// 示例 2：
//输入：root = [1,2,2,3,3,null,null,4,4]
//输出：false
//
// 示例 3：
//输入：root = []
//输出：true
//
// 提示：
// 树中的节点数在范围 [0, 5000] 内
// -10⁴ <= Node.val <= 10⁴

public class IsBalanced {
    public static class TreeNode {
      int val;
      TreeNode left;
      TreeNode right;
      TreeNode() {}
      TreeNode(int val) { this.val = val; }
      TreeNode(int val, TreeNode left, TreeNode right) {
          this.val = val;
          this.left = left;
          this.right = right;
      }
  }

    public boolean isBalanced(TreeNode root) {
        return height(root) >= 0;
    }

    private int height(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int leftHeight = height(root.left);
        int rightHeight = height(root.right);
        if (leftHeight == -1 || rightHeight == -1 || Math.abs(leftHeight - rightHeight) > 1) {
            return -1;
        }
        return Math.max(leftHeight, rightHeight) + 1;
    }
}
